The present invention pertains to phenolic antioxidant dispersions with high shelf storage stability and to the process for producing the same.
In the prior art, there is described a procedure for preparing dispersions of the polymer stabilizer, N-phenyl-N'(1,3-dimethylbutyl)-p-phenylene diamine, in a system which additionally contains oleic acid, sodium hydroxide, and water. This system is deficient in that the system has only limited shelf storage stability. Moreover, due to the high coloration of the above diamine, its dispersions have only limited applicability, e.g., in carbon black loaded resins or rubber applications or other applications in which good color performance is not required. We have now surprisingly found that dispersions of certain non-staining phenolic antioxidants, after preparation in accordance with a procedure suggested for the above diamine, are stable for a much longer period of time than the prior art diamine dispersions. Furthermore, they are suitable in applications where good initial color is required.
In U.S. Pat. No. 3,408,308, there are described emulsion concentrates of water-immiscible liquid antioxidants which are said to be remarkably stable. The antioxidants utilized in U.S. Pat. No. 3,408,308 are liquids and the order of addition of components in the preparation of the emulsion concentrates is taught to be critical, i.e., a mix of water and a fatty acid must be added to a mix of water, soap-forming base and a liquid antioxidant. The resulting product is a stable water-in-oil emulsion concentrate containing 90-95% active material (antioxidant) and is capable of self-emulsification upon dilution with water and inversion to form a stable oil-in-water emulsion. It has now been discovered that extremely stable dispersions of specific phenolic antioxidants can be prepared through the presently described technique which is applicable to solid antioxidants and in which a different method and order of component addition from that taught in U.S. Pat. No. 3,408,308 is followed.
Among techniques presently known for the preparation of emulsions or dispersions of solid antioxidants are the formation of
A. aqueous dispersions by ball milling or grinding with the use of dispersing agents and PA1 B. emulsions through an initial dissolution of the solid antioxidant in a suitable organic solvent such as xylene, toluene, a phosphite such as tris-nonylphenyl phosphite, a plasticizer such as dioctylphthalate, or some other organic vehicle. PA1 a. there is prepared PA1 b. the oil phase is then added to the water phase which is vigorously stirred and is maintained at a temperature above the temperature of the oil phase melt; PA1 c. stirring is continued for a brief period; and PA1 d. the resulting mixture is cooled to approximately room temperature using a water bath or other cooling device with occasional stirring.
The present invention has the advantage in that it obviates the need both for any ball milling, grinding and for any organic solvent. The absence of organic solvents in the preparation of the instant dispersion is particularly noteworthy in view of the many disadvantages associated with the use of such solvents, e.g., difficulty of removal, possible adverse effect on substrate, additional cost, flammability, ecological problems, etc.